That can't happen in our system. To get into Congress, you have to win whole congressional districts. That makes it very difficult for any third party to get any seats at all. The only way a 25% party could get 25% of the seats would be for its support to be concentrated in several congressional districts so that it can be a majority party in certain parts of the country.
3rd parties don't have this problem in parliamentary systems like Israel's where seats are awarded proportionally, and hence a party with even 15% can get parliamentary representation.
Third parties don't make much sense in our system. In fact they tend to have the exact opposite effect of what they are intended.
That is why we would have to go to a parliamentary system.
The only way to get third parties started in America is if you can get a very well known and well liked individual to run under its banner.
When this has happened in the past, the third party basically replaced one of the original two parties and we were soon back to a two party system again.
If Perot hadn't wigged out and dropped out and then back into the presidential race, he might have won and the Dems or Pubbies would by now have ceased to be, having been replaced by the Reform Party.